Detector assembly

ABSTRACT

An improved apparatus for operating on sheet material includes a machine having a carriage which moves a sheet during work operations and then deposits the sheet at an unloading location. A detector assembly detects when a trailing end portion of a sheet is moved from the unloading location by an unloader assembly and thereupon provides a signal to initiate operations of the machine on a next succeeding sheet. The detector assembly includes a piston and cylinder biasing assembly which moves a detector roller from an inactive position to an active position in which the detector roller is pressed against a sheet. When the trailing end of the sheet leaves the unloading location, the biasing assembly swings the detector roller upwardly to an actuated position. As the detector roller moves to the actuated position, a switch is closed to provide a signal indicating that the sheet has been removed from the unloading location. The force with which the detector roller is urged upwardly by the biasing assembly can be adjusted so that the roller is pressed upwardly with a relatively large force against heavy sheets of material and is pressed upwardly with a relatively small force against light sheets of material.

atent 91 Harris 1 Mar. 27, 1973 [54] DETECTOR ASSEMBLY [75] Inventor: Earl D. Harris, Warminster, Pa.

[73] Assignee: The Warner & Swasey Company,

Cleveland, Ohio [22] Filed: Apr. 14, 1971 [21] Appl. No.: 133,822

[52] U.S. Cl ..271/5l,27l/57 [51] Int. Cl ..B6Sh 5/06, B65h 7/00 [58] Field of Search ..27l/51, 57; 198/40; 83/79;

408/13; 101/233, 237; ZOO/61.13, 61.14,

[56] References Cited UNITED STATES PATENTS 3,545,742 12/1970 Muller ..27l/57 Primary Examiner-Edward A. Sroka Attorney-Yount and Tarolli [57] ABSTRACT An improved apparatus for operating on sheet material includes a machine having a carriage which moves a sheet during work operations and then deposits the sheet at an unloading location. A detector assembly detects when a trailing end portion of a sheet is moved from the unloading location by an unloader assembly and thereupon provides a signal to initiate operations of the machine on a next succeeding sheet. The detector assembly includes a piston and cylinder biasing assembly which moves a detector roller from an inactive position to an active position in which the detector roller is pressed against a sheet. When the trailing end of the sheet leaves the unloading location, the biasing assembly swings the detector roller upwardly to an actuated position. As the detector roller moves to the actuated position, a switch is closed to provide a signal indicating that the sheet has been removed from the unloading location. The force with which the detector roller is urged upwardly by the biasing assembly can be adjusted so that the roller is pressed upwardly with a relatively large force against heavy sheets of material and is pressed upwardly with a relatively small force against light sheets of material.

16 Claims, 8 Drawing Figures Patented 'March 27, 1973 2 Sheets-Sheet 1 IN VE'IV TOR Mm k EARL 0 HARP/5 DETECTOR ASSEMBLY The present invention relates to an apparatus for operating on sheet material and more particularly to an apparatus in which a detector assembly detects when a sheet of material is removed from a machine.

Sheet material has heretofore been unloaded from punch presses and other machines manually or by means of an unloader assembly, such as the one shown in U.S. Pat. No. 3,358,853 to Thomas et al. Although unloader assemblies similar to the one disclosed in the aforementioned Thomas patent facilitate the unloading of a machine, the speed of operation of a punch press or other machine for working on sheet material is enhanced when an unloader assembly is automatically activated by tape controls for the machine at the end of an operating cycle in the manner disclosed and claimed in copending application Ser. No. 133,873, filed by Joseph A. Linkus on Apr. 14, 1971 and entitled Unloader Assembly; While the tape controlled initiation of an unloading cycle in the manner disclosed in the aforementioned Linkus application represents a substantial improvement over a known apparatus in which the unloading cycle was manually initiated at the end of an operating cycle, high speed operation of 'a punch press or other machine is promoted by the initiating of operations on a next succeeding sheet as soon as the preceding sheet has been removed from the machine. However, the next succeeding sheet should not be loaded into the machine until the preceding sheet has been removed from the machine to prevent interference between the sheets.

The present invention provides an improved detector assembly which is activated by controls for the machine at the beginning of an unloading cycle to detect when a sheet has been unloaded from the machine. Upon detecting the unloading of a sheet, the detector assembly immediately signals the controls for the machine to initiate the loading of the next succeeding sheet into the machine. By providing this cooperation between the detector assembly and the controls for the machine, the total time required to process a plurality of sheets tends to be minimized.

Accordingly, it is an object'of this invention to provide a new and improved apparatus for operating on sheet material and which includes a detector assembly for detecting when one sheet of material has been removed from a machine and for thereupon'providing a signal to initiate the loading of a next succeeding sheet into the machine. v

Another object of this invention is to provide a new and improved apparatus for operating on sheet material and which includes a detector assembly detecting a trailing end portion of a sheet which has been partially cut away and into which holes have been punched.

Another object of this invention is to provide a new and improved apparatus for operating on sheets of material including a machine for performing work operations on each of the sheets of material in turn at a work area and positioning asheet of material at an unloading location upon completion of work operations on the sheet of material, an unloader assembly which removes the sheet of material from the machine, and a detector assembly for detecting when a sheet of material is removed from the machine by the unloader assembly and wherein the detector assembly is operated from an inactive condition in which it is ineffective to detect the removal of a sheet of material from the machine to an active condition in which the detector assembly is effective to detect the removal of a sheet of materialfrom the machine by a control assembly upon a depositing of a sheet of material at the unloading location by the machine.

Another object of this invention is to provide a new and improved apparatus for operating on sheets of material wherein the apparatus includes a control assembly for controlling the operation of a machine which performs work operations on the sheet material and a detector assembly for detecting when the trailing end portion of a sheet of material is removed from the machine by an unloader assembly, the detector assembly being operable to provide a signal to the control apparatus upon movement of the trailing end portion of the sheet from the machine.

Another object of this invention is to provide a new and improved apparatus for operating on sheets of material which are moved to and from an unloading location and wherein the apparatus includes a detector member which is pressed against the surface of a sheet of material at the unloading location by a biasing means which is effective to move the detector member to an actuated or activated position upon movement of a trailing end portion of the sheet material from the unloading location.

Another object of this invention is to provide a new and improvedapparatus set forth in the next preceding object and wherein the pressure with which the detector member urged against the sheet material is adjustable to enable the detector assembly to be used with sheets of material of different weights.

These and other objects and features of the invention will become more apparent upon a consideration of the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a schematic illustration depicting the relationship between a tape controlled turret punch press, a detector assembly, and'an unloader assembly;

FIG. 2 is an elevational view, taken generally along the line 2-2 of FIG. 1, illustrating the construction of the detector assembly;

FIG. 3 is a fragmentary plan view, taken generally along the line 33 of FIG. 2, further illustrating the construction of the detector assembly;

FIG. 4 is an end view, taken generally along the line 4-4 of FIG. 2, illustrating the detector assembly in an inactive condition in which the detector assembly is ineffective to detect the removal of a sheet of material from the punch press of FIG. 1;

FIG. 5 is a sectional view, taken generally along the line 5-5 of FIG. 2, illustrating the detector assembly in an active condition in which a detector roll .is pressed against a sheet by a piston and cylinder biasing assembly;

FIG. 6 is a fragmentary sectional view, generally similar to FIG. 5, illustrating the detector assembly in an actuated condition to which it is operated by the biasing assembly upon movement of a trailing end portion of a sheet past the detector roll;

FIG. 7 is an end view, generally similar to FIG. 4, illustrating the actuation of a switch by the detector assembly upon movement of the detector assembly to the actuated condition of FIG. 6; and

FIG. 8 is a schematic illustration of a control apparatus for the punch press and the detector assembly.

Although a detector assembly 10 constructed in accordance with the present invention can be utilized in association with the different types of machines, the detector assembly is illustrated in FIG. 1 in association with a tape controlled turret punch press 12 of known construction. The punch press 12 includes a plurality of workholders 14 which grippingly engage a piece of sheet metal 16 which is supported on a work table 18. The workholders 14 are of a known self-adjusting pneumatically actuated type and are mounted on a cross slide 22 which is movable back and forth along ways 26 to position the sheet 16 relative to a turret 28 which holds a plurality of tools for punching holes 30 in the sheet. The cross slide 22 and table 18 are movable along crossways 34 and 36 to position the sheet 16 relative to the turret 28.

The punch press 12 is operated in accordance with a predetermined program punched on a tape 40 (FIG. 8) which is read by a reader 42. The reader 42 activates a control apparatus 44 to index the turret 28 (FIG. 1) and move the table 18 in accordance with the program on the tape 40. Once the sheet 16 has been punched, the sheet is moved to an unloading location or position in which a leading end portion 48 of the sheet extends beyond the detector assembly 10 toward an unloader assembly 50 (see FIG. Although many different types of unloader assemblies could be utilized in association with the detector assembly and punch press 12, the unloader assembly 50 is advantageously constructed in the manner set forth in the aforementioned Linkus application. Once the sheet 16 has been moved to the unloading location, the tape 40 is indexed and the reader 42 activates the detector assembly 10 to initiate operation of the unloader assembly 50. The unloader assembly 50 then grips the leading end portion 48 of the sheet 16 with a pair of members, such as the rollers 54 and 56 (see FIG. 5).

Continued operation of the unloader assembly 50 pulls the sheet 16 from the punch press 12 and transports the sheet to a suitable receiving location. It should be noted that as the trailing end portion 60 of the sheet 16 is moved out of the punch press 12 and past the detector assembly 10, the detector assembly 10 is operated to the actuated condition of FIGS. 6 and 7. Operation of the detector assembly 10 to the actuated condition operates a limit switch 64 (see FIGS. 4 and 7) in control circuitry 66 (FIG. 8) to signal the machine control apparatus 44 that the sheet 16 has been completely withdrawn from the punch press 12 by the unloader assembly 50. The machine control apparatus 44 then effects an indexing of the tape 40 by the reader 42 to initiate a loading of the next succeeding sheet into the punch press 12 by a suitable loader assembly (not shown).

Since the detector assembly 10 is operated to the actuated condition of FIGS. 6 and 7 in response to movement of the trailing end portion 60 of the sheet 16 past the detector assembly, the sheet 16 is completely withdrawn or unloaded from the punch press 12 before loading of the next succeeding sheet onto the work table 18. In this manner, interference is prevented between successive sheets. However, the next succeeding cycle of operation of the punch press 12 is initiated as soon as the preceding sheet 16 is removed from the punch press by operation of the unloader assembly 50 to thereby tend to minimize the elapsed time required for processing each ofthe sheets.

From the foregoing, it is apparent that upon completion of a punching cycle by the press 12 on the sheet 16, the carriage 22 is moved toward the right' (as viewed in FIG. 1) in accordance with a program punched in the tape 40. When the leading end portion 48 of the sheet 16 extends beyond the detector assembly 10 to a position which can be readily engaged by the unloader assembly 50, the tape reader 42 and controls 44 interrupt rightward movement of the carriage 22. The workholders 14 are then released in a known manner and the carriage 22 is withdrawn toward the left.

Contemporaneously with this leftward movement of the carriage 22, the tape reader 42 (FIG. 8) is indexed and a punched code on the tape 40 is read. This results in the transmission of a signal to the machine control apparatus 44 to effect operation of the detector assembly 10 from the inactive condition of FIG. 4 to the active or detecting condition of FIG. 5. This is accomplished by retracting a piston and cylinder biasing assembly 70 to press a detector member or roller 74 against a lower or bottom surface 76 of the sheet 16 (FIG. 5). As the sheet 16 is withdrawn from the punch press 12 by operation of the unloader assembly 50, the roller 74 is continuously urged against and rolls along the lower surface 76 of the sheet-to thereby support the sheet with a support roller 80 which extends parallel to the detector roller 74. The detector roller 74 extends across the width of the sheet 16 so that the detector assembly 10 is not erroneously actuated by a hole or cutaway portion of the sheet.

Upon movement of the trailing end portion of the sheet 60 past the detector assembly 10, the biasing as sembly 70 pivots the detector roller 74 upwardly about the longitudinal axis of the support roller 80 from the active or detecting position of FIG. 5 to the actuated position of FIG. 6. In the actuated position, the detector roller 74 is located above the upper support surface 84 of the table 18 and the bottom surface 76 of the sheet 16. Movement of the detector roller 74 to the actuated position of FIG. 6 moves an actuator arm 88 downwardly to actuate the limit switch 64 in the manner illustrated in FIG. 7. Actuation of the limit switch 64 energizes a solenoid 96 to operate a control valve 98 (FIG. 8) to extend the biasing assembly 70 and return the detector roller 74 to the inactive position of FIG. 4. As the detector roller 74 moves downwardly toward the inactive position, its movement is retarded by a shock or impact absorber 100 to prevent excessive rebounding of the detector roller.

In addition, operation of the limit switch 64 provides a signal which indicates to the control apparatus44 that the sheet 16 has been completely removed from the punch press 12. Upon receiving this signal, the machine control apparatus 44 transmits a signal to the tape reader 42 to index the tape 40. It is contemplated that the next step in the program on the tape 40 will initiate the loading and next operating cycle of the punch press 12 to process a next succeeding sheet of material in accordance with the program punched on the tape. It should be noted that the tape reader 42 and control ap- 108, 110, and 112 which are rotatably connected with the mounting plate 104 by a plurality of cantilevered brackets 114, 116, 118, and 120 (see FIGS. 2 and 3). The sections 106 and 108 of the detector roller 74 are connected with the support brackets 114-120 for pivotal movement about the longitudinal axis of the support roller'80 by brackets 124, 126 and 128 which are interconnected by a longitudinally extending support channel 129 (FIGS. 2 and 4). Thus, the detector roller sections 106 and 108 are pivotally mounted for arcuate movement about the longitudinal axis of the support roller 80 from the inactive position of FIG. 4 through the activated or detecting position of FIG. 5 to the actuated position of FIG. 6 under the influence of the biasing assembly 70. It should be noted that the sections 106 and 108 of the detector roller 74 have a combined length which is approximately equal to the width of the sheet 16 to prevent the detector roller 74 from being moved to the actuated position when a hole or cut-away portion of the sheet passes over the detector roller.

In the specific preferred embodiment of the invention illustrated in the drawings, the biasing assembly 70 is a double-acting pneumatic piston and cylinder assembly. The piston and cylinder assembly 70 includes a cylinder 130 which is pivotally mounted at a connection 132 to a support bracket 134 (see FIG. 5) connected to the mounting plate 104. A piston rod 138 is pivotally connected with an arm 140 whichis in turn connected with the roller support bracket 126 and support channel 129. Therefore, upon initial retraction of the piston and cylinder assembly 70, the detector roller 74 is pivoted upwardly from the inactive position of FIG. 4 to the active or detecting position of FIG. 5. Continued retraction of the piston and cylinder assembly 70 moves the roller 74 from the detecting position shown in FIG. 5 to the actuated position shown in FIG. 6. Similarly, upon extension of the piston and cylinder assembly 70, the detector roller 74 is pivoted downwardly from the actuated position of FIG. 6 through the detecting position of FIG. 5 to the inactive position of FIG. 4. As the detector roller 74 approaches the inactive position of FIG. 4, its movement is retarded by engagement of the support channel 129 with the shock absorber 100.

The piston and cylinder assembly 70 is selectively operated between the extended and retracted conditions by' the control valve 98 (FIGS. 2 and 8). When the detector roller 74 is in the inactive position in FIG. 4 and the pistonand cylinder assembly 70 is fully extended, air under pressure is conducted through conduit 144 to the lower end portion of the cylinder 130 to urge a piston 146 (FIG. 8) upwardly in the cylinder 130. When the detector roller 74 is to be moved from the inactive position of FIG. 4 to the active or detecting position of FIG. 5, the solenoid 96 is energized to move the valve 98 toward the left (as viewed in FIG. 8) against the influence of a return spring 150. This operates the valve 98 to port fluid under pressure through a conduit 154 to the upper end of the cylinder 130. The pressurized fluid causes the piston 146 to move downwardly in the cylinder 132 to effect a pivoting movement of the detector roller 74 upwardly from the inactive position (FIG. 4) to the active position (FIG. 5) in which the detector roller engages the lower or detecting surface 76 of the sheet 116. While the solenoid 96 is energized to maintain the valve 98 in an operated condition, air pressure against the piston 146 continuously urges the piston downwardly in the cylinder 130. Therefore, when the trailing end portion of the sheet 16 moves past the detector roller 74, the piston and cylinder assembly is further retracted to pivot the detector roller upwardly to the actuated position of FIG. 6.

It is contemplated that metal sheets of many different thicknesses and weights will be operated on by the punch press 12. Since the weight of the sheet 16 will vary, a pressure regulator 160 is provided in the line 154 between the valve 98 and the upper end of the cylinder (see FIG. 2). The pressure regulator is of a known construction and is adjustable to regulate the fluid pressure communicated to the cylinder 130 to thereby enable the force with which the piston 146 is urged downwardly to be varied. This enables the force with which the detector roller 74 is urged upwardly to be varied in accordance with the weight of the stock being sensed. A gauge 162 is advantageously associated with'the pressure regulator 160 to indicate the pressure of the air flowing into the cylinder 130.

From the foregoing it is apparent that during operation of the punch press 12, the tape 40 is read by the reader 42 to operate the control apparatus 44 to position and punch the sheet 16 in accordance with the program recorded on the tape. After the sheet 16 has been processed. in accordance with the program on the tape 40, the tape is indexed and a signal is transmitted to the control apparatus 40 to cause the cross slide 22 to move the sheet 16 to the unloading position with the leading end portion 48 of the sheet extending beyond the detector assembly 10 (see FIG. 5). When the sheet 16 has been moved to the unloading location; the tape 40 is again indexed and a signal is transmitted to the control apparatus 44 to effect an engaging of the sheet by the unloader 50 and a releasing of the sheet by the workholders 14. The control apparatus 44 also effects operation of the detector assembly 10 to the detecting condition of FIG. 5 in response to this signal from the tape reader 42.

The control apparatus 44 effects activation of the piston and cylinder assembly 70 to move the detector roller 74 from the inactive position of FIG. 4 to the detecting or active position of FIG. 5 by energizing the solenoid 96 to shift the control valve 98 against the influence of the return spring 150. To energize the solenoid 96, the control apparatus 44 closes contacts in the control circuitry 66 to energize a relay 172. Energization of the relay 172 opens its normally closed interlock contacts 174 in the control apparatus 44 to prevent the erroneous initiation of an operating cycle by the control apparatus 44 until after the sheet 16 has been completely removed or unloaded from the punch press 12. Energization of the relay 172 also closes normally open contacts 175 and 176 to energize the solenoid 96 and complete the holding circuit for the relay 172. Therefore, a momentary closing of contacts 170 results in the relay 172 and solenoid 96 remaining energized to inaintain the rod end of the cylinder 130 in communication with a source of air pressure through the valve 98. This causes the piston rod 138 to be continuously biased downwardly (as viewed in FIG. to urge the detector roller 74 upwardly against the lower surface 76 of the sheet 16.

When the trailing end portion 60 of the sheet is moved past the. detector assembly due to operation of the unloading assembly 50, the detector roller 74 is sembly 70 is fully retracted (see FIG. 6). However, this upward movement of the detector roller 74 results in the limit switch 64 being actuated by the arm 88 (see FIG. 7). The limit switch 64 is connected in the energizing circuit or the relay 172 (FIG. 8). Therefore, as soon as the detector roller 74 is pivotedto the actuated position of FIGS. 6 and 7 in response to the unloading of the sheet 16, the relay 172 is de-energized and the relay contacts 175 and 176 are opened to de-energize the solenoid 96. Of course, de-energization of the solenoid 96 enables the return spring 150 to move the valve 98 back to the normal position illustrated in FIG. 8. When the valve 98 is in the normal position of FIG. 8, the rod end of the cylinder 130 is connected in communication with drain while the head or lower end of the cylinder is connected with the source of air pressure to thereby extend the piston and cylinder assembly 70 to return the detector roller 74 from the actuated position of FIGS. 6 and 7 to the inactive position of FIG. 4.

Once the trailing end of the sheet 16 has moved past the detector assembly 10, the next succeeding sheet should immediately be loaded into the punch press 12.

Therefore, upon movement of the detector roller 74 to the inactive condition, the interlock contacts 174 are again closed to render an interlock circuit in the control apparatus 44 ineffective. The interlock contacts 174 are closed by de-energization of the relay 172 upon opening of the limit switch 64. This completes a circuit to initiate the sending of a signal from the control apparatus 44 to the tape reader 42 to index the tape 40 and initiate the next operating cycle of the punch press 12.

In view of the foregoing description, it is apparent that the operation of the punch press 10 is expedited by the use of the detector assembly 10. This is because the detector assembly 10 prevents the loading of a sheet into the punch press 12 before the preceding sheet has been completely withdrawn or unloaded from the punch press. However, once the preceding sheet 16 has 22. The biasing assembly continuously presses the roller 74 against the lower surface 76 of the sheet 16. Therefore, when the trailing end portion 60 of the sheet is pulled out of the punch press 12 past the detector roller 74, the biasing assembly pivots the detector roller upwardly to the activated condition and effects actuation of the switch 64. Actuation of the switch 64 deenergizes the relay 172 to close its contacts 174 and thereby signal the control apparatus 44 that the sheet has been withdrawn from the punch press 12.

Having described a specific preferred embodiment of the invention, the following is claimed:

1. An apparatus for sequentially operating on sheets of material, said apparatus comprising a machine for performing work operations on each of the sheets of material in turn at a work area and positioning a sheet of material at an unloading location upon completion of work operations on the sheet of material, unloader means for engaging a sheet of material at the unloading location and removing the sheet of material from said machine, detector means for detecting when a sheet of material is removed from said machine by said unloader means, said detector means being operable between an inactive condition in which said detector means is ineffective to detect the removal of a sheet of material from said machine and an active condition in which. said detector means is effective to detect removal of a sheet of material from said machine, and control means for effecting operation of said detector means from the inactive condition to the active condition upon the depositing of a sheet of material at the unloading location by said machine.

2. An apparatus as set forth in claim 1 wherein said control means further includes means for effecting operation of said detector means from the active condition to the inactive condition upon removal of a sheet of material from the unloading location.

3. Apparatus as set forth in claim 2 wherein said control means renders said machine ineffective to move a next succeeding sheet of material to the work area until said detector means provides a signal to said control means indicating that the preceding sheet of material has been removed from the unloading location by said unloader means.

4. An apparatus as set forth in claim 1 wherein said detector means includes a detector surface which is movable from a first position disposed in abutting engagement with a surface of a sheet of material at the unloading location to a second position upon movement of a trailing end portion of a sheet of material from the unloading location, biasing means for continuously urging said detector surface toward the second position when said detector means is in the active condition, and means for providing the signal to said control means upon movement of said detector surface from the first position to the second position.

i 5. An apparatus as set forth in claim 4 wherein said control means includes means for rendering said biasing means ineffective to urge said detector surface to the second position and to effect operation of said detector means from the active condition to the inactive condition in response to movement of said detector surface from the first position to the second position.

6. An apparatus as set forth in claim 5 wherein said control means includes means for adjusting the force with which said detector surface is urged from the first position to the second position with variations in the weight of the sheet material operated on by said apparatus.

7. 7 An apparatus as set forth in claim 6 wherein said biasing means includes a piston and cylinder assembly and means for connecting said piston and cylinder assembly with a source of fluid under pressure, said force adjusting means including means for regulating the pressure at which fluid is communicated to said piston and cylinder assembly from said source of fluid under pressure.

8. An apparatus as set forth in claim 1 wherein said control means includes means for rendering said machine ineffective to move a next succeeding sheet of material to the work area while a proceeding sheet of material is at the unloading location and for rendering said machine effective to move the next succeeding sheet of material to the work area in response to detection of the removal of the proceeding sheet of material from the unloading location by said detector means.

9. An apparatus as set forth in claim 1 wherein said detector means includes a detector member and means for moving said detector member between first and second positions upon operation of said detector means between said active and inactive conditions, said apparatus further including shock absorber means for minimizing any tendency of said detector member to rebound from one of said positions toward the other of said positions upon operation of said detector means between said active and inactive conditions.

10. An apparatus for operating on sheets of material, said apparatus including means for moving sheets of material to and from an unloading location, detector means for detecting when the trailing end portion of a sheet of material is moved from the unloading location, said detector means including a detector member movable between an inactive position on one side of a detecting plane, a first'active position in which saiddetector member is disposed in abutting engagement with a surface of a sheet of material located in the detecting plane, and a second active position in which at least a portion of said detector member is disposed on aside of the detecting plane opposite from the one side, and biasing means for moving said detector member from the inactive position to the first active position and for urging said detector member toward the second active position to press said detector member against the surface of a sheet of material which is located in the detecting plane, said biasing means being operable to move said detector member from the first active position to the second active position upon movement of a trailing end portion of the sheet of material from the unloading location, and control means for rendering member from the second active position to the inactive position in response to movement of said detector member to the second active position.

11. An apparatus as set forth in claim 10 wherein said biasing means includes a piston and cylinder assembly and said control means includes valve means for connecting at least one end portion of said piston and cylinder assembly in fluid communication with a source of fluid under pressure to effect operation of said iston and cylinder assembly to move said detector mem er between the inactive position and the first and second active positions.

12. Apparatus as set forth in claim 11 wherein said control means includes means for varying the fluid pressure communicated from the source of fluid under pressure to said piston and cylinder assembly to vary the force with which said detector member is pressed against the sheet material by said biasing means.

13. Apparatus as set forth in claim 12 wherein said valve means is operable to port fluid to said one end portion of said piston and cylinder assembly to effect movement of said detector member from the inactive position the first active position and to effect movement of said detector member from the first active position to the second active position, aid valve means also being operable to port fluid to an end portion of said piston and cylinder assembly to effect movement of said detector member from the second active position to the inactive position.

14. Apparatus as set forth in claim 13 further including shock absorber means for retarding movement of said detector member as said detector member moves from the second active position to the active position to tend to minimize any tendency of said detector member to rebound from the inactive position toward the first active position upon movement of said detector member to the inactive position.

15. Apparatus as set forth in claim 10 wherein said detector member is a roller'having a peripheral surface which is disposed in rollingengagement with a lower surface of esheet of material as the sheet of material is moved from the unloading location, said biasing means being operable to urge said rollerupwardly from the first active position toward the second active position to thereby at least partially support the sheet material as it is moved from the unloading location.

16. An apparatus as set forth in claim 15 wherein said control means includes means forvarying the force with which said roller is urged upwardly against the sheet material by said biasing means with variations in the weight of the sheet material operated on by said apparatus.

i i i i 

1. An apparatus for sequentially operating on sheets of material, said apparatus comprising a machine for performing work operations on each of the sheets of material in turn at a work area and positioning a sheet of material at an unloading location upon completion of work operations on the sheet of material, unloader means for engaging a sheet of material at the unloading location and removing the sheet of material from said machine, detector means for detecting when a sheet of material is removed from said machine by said unloader means, said detector means being operable between an inactive condition in which said detector means is ineffective to detect the removal of a sheet of material from said machine and an active condition in which said detector means is effective to detect removal of a sheet of material from said machine, and control means for effecting operation of said detector means from the inactive condition to the active condition upon the depositing of a sheet of material at the unloading location by said machine.
 2. An apparatus as set forth in claim 1 wherein said control means further includes means for effecting operation of said detector means from the active condition to the inactive condition upon removal of a sheet of material from the unloading location.
 3. Apparatus as set forth in claim 2 wherein said control means renders said machine ineffective to move a next succeeding sheet of material to the work area until said detector means provides a signal to said control means indicating that the preceding sheet of material has been removed from the unloading location by said unloader means.
 4. An apparatus as set forth in claim 1 wherein said detector means includes a detector surface which is movable from a first position disposed in abutting engagement with a surface of a sheet of material at the unloading location to a second position upon movement of a trailing end portIon of a sheet of material from the unloading location, biasing means for continuously urging said detector surface toward the second position when said detector means is in the active condition, and means for providing the signal to said control means upon movement of said detector surface from the first position to the second position.
 5. An apparatus as set forth in claim 4 wherein said control means includes means for rendering said biasing means ineffective to urge said detector surface to the second position and to effect operation of said detector means from the active condition to the inactive condition in response to movement of said detector surface from the first position to the second position.
 6. An apparatus as set forth in claim 5 wherein said control means includes means for adjusting the force with which said detector surface is urged from the first position to the second position with variations in the weight of the sheet material operated on by said apparatus.
 7. 7 An apparatus as set forth in claim 6 wherein said biasing means includes a piston and cylinder assembly and means for connecting said piston and cylinder assembly with a source of fluid under pressure, said force adjusting means including means for regulating the pressure at which fluid is communicated to said piston and cylinder assembly from said source of fluid under pressure.
 8. An apparatus as set forth in claim 1 wherein said control means includes means for rendering said machine ineffective to move a next succeeding sheet of material to the work area while a preceeding sheet of material is at the unloading location and for rendering said machine effective to move the next succeeding sheet of material to the work area in response to detection of the removal of the proceeding sheet of material from the unloading location by said detector means.
 9. An apparatus as set forth in claim 1 wherein said detector means includes a detector member and means for moving said detector member between first and second positions upon operation of said detector means between said active and inactive conditions, said apparatus further including shock absorber means for minimizing any tendency of said detector member to rebound from one of said positions toward the other of said positions upon operation of said detector means between said active and inactive conditions.
 10. An apparatus for operating on sheets of material, said apparatus including means for moving sheets of material to and from an unloading location, detector means for detecting when the trailing end portion of a sheet of material is moved from the unloading location, said detector means including a detector member movable between an inactive position on one side of a detecting plane, a first active position in which said detector member is disposed in abutting engagement with a surface of a sheet of material located in the detecting plane, and a second active position in which at least a portion of said detector member is disposed on a side of the detecting plane opposite from the one side, and biasing means for moving said detector member from the inactive position to the first active position and for urging said detector member toward the second active position to press said detector member against the surface of a sheet of material which is located in the detecting plane, said biasing means being operable to move said detector member from the first active position to the second active position upon movement of a trailing end portion of the sheet of material from the unloading location, and control means for rendering said biasing means effective to move said detector member from the second active position to the inactive position in response to movement of said detector member to the second active position.
 11. An apparatus as set forth in claim 10 wherein said biasing means includes a piston and cylinder assembly and said control means includes valve means for connecting at least one end portion of said piston and cYlinder assembly in fluid communication with a source of fluid under pressure to effect operation of said piston and cylinder assembly to move said detector member between the inactive position and the first and second active positions.
 12. Apparatus as set forth in claim 11 wherein said control means includes means for varying the fluid pressure communicated from the source of fluid under pressure to said piston and cylinder assembly to vary the force with which said detector member is pressed against the sheet material by said biasing means.
 13. Apparatus as set forth in claim 12 wherein said valve means is operable to port fluid to said one end portion of said piston and cylinder assembly to effect movement of said detector member from the inactive position the first active position and to effect movement of said detector member from the first active position to the second active position, aid valve means also being operable to port fluid to an end portion of said piston and cylinder assembly to effect movement of said detector member from the second active position to the inactive position.
 14. Apparatus as set forth in claim 13 further including shock absorber means for retarding movement of said detector member as said detector member moves from the second active position to the active position to tend to minimize any tendency of said detector member to rebound from the inactive position toward the first active position upon movement of said detector member to the inactive position.
 15. Apparatus as set forth in claim 10 wherein said detector member is a roller having a peripheral surface which is disposed in rolling engagement with a lower surface of e sheet of material as the sheet of material is moved from the unloading location, said biasing means being operable to urge said roller upwardly from the first active position toward the second active position to thereby at least partially support the sheet material as it is moved from the unloading location.
 16. An apparatus as set forth in claim 15 wherein said control means includes means for varying the force with which said roller is urged upwardly against the sheet material by said biasing means with variations in the weight of the sheet material operated on by said apparatus. 